A raindrop detector that detects the quantity of waterdrops adhering to a window glass has been known, for example, as indicated by patent literature 1. The raindrop detector includes a waterdrop detecting portion that detects the quantity of waterdrops adhering to the window glass at a predetermined interval, and a change rate calculating portion that calculates the rate of change of the quantity of the waterdrops in each predetermined interval detected by the waterdrops detecting portion. The raindrop detector further includes a determining portion that determines an adhering state of waterdrops to the window glass based on the rate of change of the quantity of the waterdrops calculated. When the rate of change of the quantity of waterdrops is equal to or greater than a predetermined rate of increase, the determining portion determines that the window glass is in a condensed state in which the waterdrops adhering to the window glass are condensed on the window glass.